Orbital weldheads for use in gas tungsten arc welding (GTAW) can provide flexibility and accuracy in welding tubular joints for a variety of applications by using a simple single pass orbital motion of the weld torch around the weld joint for thin walled tubes. However, to perform GTAW of thickwalled tubes and pipes utilizing automatic orbital welding techniques, two orthogonally related motions of the weld torch must be simultaneously controlled by means of an integrated electro-mechanical system. The one motion is directed normal to, i.e., closer to or farther from, the weld part surface along the tungsten electrode centerline, commonly referred to as automatic voltage control or AVC, and the other motion is directed orthogonal to this in the direction of the centerline axis of the weld part, i.e., back and forth along the length of the pipe, commonly referred to as oscillation. Performing these functions in a confined area requires the design of an integrated unit that is both miniature but rugged and one that is properly designed to function in a closed-loop servo manner with maximization of the servo-control response to the AVC primarily and to the oscillation secondarily. In order to accomplish this the mass of the AVC mechanism must be minimized to reduce lagging inertial effects and the drive train smoothness maximized to promote unhindered motion.
To date, integrated units have emphasized, instead, the reverse of the above resulting in the mediocre performance of the AVC control that requires quick response. This is because it is much easier to mechanize the integrated unit with a motorized motion directly on the GTAW torch cross-seam adjustment, thus becoming the motorized oscillation, and then a motorized motion of the resulting mechanism on the AVC. This then results in a large AVC-controlled mass which includes the oscillation motor together with its accompanying slides and structure. In an exemplary embodiment, the present invention minimizes the mass to be controlled by the AVC first and then includes this mass into the oscillation motion that does not have to be as mechanically responsive.